Technical Field
The present disclosure relates to a continuously operating solar thermal absorption cooling system that prevents crystallization of an absorbent within an absorption-refrigerant solution and a method of providing a continuous cooling to at least one load using the system.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
High ambient temperatures have a direct impact on cooling demand; almost all buildings are cooled by conventional electricity powered air conditioning systems, which consume a large amount of electrical power. The development of an air conditioning system or general cooling system that may run on an alternative source of energy will save electrical energy, which is primarily produced by burning fossil fuels. Such systems will significantly aid in the reduction of carbon emission, thus reducing environmental pollution and global warming effects. Out of various renewable energy sources, solar energy proves to be the best candidate because of the coincidence of the maximum cooling load with the period of maximum solar radiation input. Solar energy is a free energy source which can be effectively used for many domestic and industrial applications including refrigeration and air conditioning.
Solar energy can be used to power cooling systems in two ways. First, solar energy can be converted into electricity by using photovoltaic cells, and then used to operate a conventional vapor compression cooling system. Second, solar energy can be used to heat a working fluid and generate a refrigerant in a generator of a vapor sorption (absorption or adsorption) cooling system. Solar electric cooling systems using photovoltaic cells are more expensive than solar thermal systems. Further evaluation of solar thermal cooling systems (absorption compared to adsorption systems) reveals that the absorption system is ˜50% cheaper than the adsorption system in terms of capital cost.
The use of solar energy as a low grade thermal energy for absorption cycles has gained considerable attention among researchers over the last few decades. The major working pairs employed for solar absorption systems are lithium bromide-water (LiBr—H2O) and water-ammonia (H2O—NH3). Although an ammonia-water system can produce cooling effects below zero degrees Celsius, it has certain disadvantages related to its lower coefficient of performance (COP), higher generator inlet temperature, higher pumping power and a more complex system that places restrictions on it uses in various applications.
Solar energy can be effectively utilized for cooling purposes by using these absorption systems. However, the greatest challenge in utilizing solar energy for uninterrupted cooling is its unavailability during the nighttime. Solar collectors are only able to gather energy during daylight hours at times of high solar heat input. In order to meet the uninterrupted cooling needs and extend the operation hours of these systems, they must be integrated with a storage system and energy storage tanks that will compensate for needs during nighttime operation and/or times of low solar heat input.
The analysis of storage systems for solar cooling purposes has been an important research topic. Research has indicated that thermal storage integrated into solar cooling systems increases the cooling availability and capacity, while improving the overall performance. Results have indicated that a reasonable sized cold storage tank can reduce the capacity of the chiller, without significantly affecting the system's energy performance. Similarly, analysis has indicated that a continuously operating solar powered absorption system with refrigerant storage is a suitable alternative device. Systems that must operate at high ambient temperatures and times of high thermal input must be able to efficiently gather enough energy (i.e. hot thermal, cold thermal, refrigerant and combinations) to provide for continuous cooling. Operations at these conditions can result in performance degradation, crystallization of the adsorbent, as well as high water consumption for heat rejection to the environment. Preventing crystallization in solar-powered simple salt and water systems, such as lithium bromide salt and water, is one of the most important design factors necessary to improve and maximize the system's performance.
In view of the forgoing, one object of the present disclosure is to provide an alternate design for a day and night continuously operating solar powered absorption cooling system that significantly reduces or eliminates absorbent crystallization. The system possesses hybrid storage (cold and refrigerant) facilities for continuous (24 hours a day) operation and an excess heat storage tank governed by two temperature control valves that control and prevent crystallization. A further aim of the present disclosure is to provide a method for continuously cooling at least one load using the system as described herein.